The iambic trimeter derives its name from its essential shape, which is three metrical units (hence trimeter) which are each basically iambic in form. The iambic metron has the following shape (where the x is an anceps, the - is a longum, and the u is a brevis):
Hence, reversing the current running though a wire will have the affect of reversing the direction of the magnetic force at a point some distance away from the wire. The affect that this has on the overall magnetic field depends on the shape of the wire.
The magnet is inducing an eddy current in the copper coil a tube is just a coil with one turn, the electric current flowing in the tube creates a magnetic field which then interacts with the field of the magnet either attracting or repelling depending on the direction of movement.